1. Field of the Invention
The present invention relates to a digital video camera and, more particularly, to an apparatus suitably used in a video camera apparatus for converting an analog video signal obtained by an image pickup element into a digital video signal and performing digital signal processing.
2. Related Background Art
FIGS. 1A and 1B show a conventional video camera apparatus for A/D-converting an analog signal output from a solid-state image pickup element, and performing signal processing in a digital form. Referring to FIGS. 1A and 1B, a video signal obtained via a lens element 1, a solid-state image pickup device 2, a correlation double sampling circuit 3, and a gain adjustment circuit 4 is sampled by an A/D converter 5 to be converted into a digital signal.
The sampled digital signal is supplied to a digital signal processing circuit 6. The digital signal processing circuit 6 generates a digital luminance signal and digital color-difference signals from the input digital signal. The digital luminance signal generated by the digital signal processing luminance signal via a D/A converter 12 and a low-pass filter 13.
The digital color-difference signals are converted into band-limited analog color-difference signals via D/A converters 35 and 36 and low-pass filters 37 and 38. Furthermore, the analog color-difference signals are supplied to a modulation circuit 39 to be converted into an analog chrominance signal. The analog chrominance signal is supplied to a digital signal recording device 21 together with the analog luminance signal. The processing so far is executed at the sampling frequency of the image pickup element.
When YC-separated input signals are externally input as a video signal, these signals are respectively input to switch circuits 8 and 9. When a composite video signal VIDEO is input, the signal VIDEO is separated into luminance and chrominance signals by a luminance/chrominance separation circuit 7, and the separated signals are input to the switch circuits 8 and 9. One of these YC-separated input signals and the composite video signal is selected by the switch circuits 8 and 9.
The analog luminance and color-difference signals from a camera and externally input analog luminance and color-difference signals are selected by switch circuits 14 and 15. The frequency band of the analog luminance signal is limited by a low-pass filter 17. The band-limited analog luminance signal is supplied to an A/D converter 18 to be converted into a digital luminance signal.
The analog chrominance signal is converted into analog color-difference signals by a demodulation device 40, and the analog color-difference signals are then converted into digital color-difference signals by A/D converters 41 and 42. In this case, the A/D conversion is performed at the sampling frequency of a digital VTR.
The digital signal recording device records the digital luminance and color-difference signals, which are converted, as described above, on a magnetic tape 22. Thus, a digital video signal is recorded.
At this time, switch circuits 25 and 26 are switched to the REC side, and the analog luminance and chrominance signals are selected and output by the switch circuits 25 and 26. An EVF 33 performs a display operation based on the output luminance and chrominance signals for monitoring an image pickup operation.
In a reproduction mode, the digital signal recording device 21 generates digital reproduced luminance and color-difference signals from a signal reproduced from the magnetic tape 22. Of these signals, the reproduced luminance signal is converted into an analog luminance signal by a D/A converter 23 which operates at the sampling frequency of the digital VTR, and thereafter, the frequency band of the analog luminance signal is limited by a low-pass filter 24, thus obtaining an analog reproduced luminance signal.
On the other hand, the digital color-difference signals are converted into analog color-difference signals by D/A converters 28 and 29 which operate at the sampling frequency of the digital VTR. The frequency bands of these analog color-difference signals are then limited by low-pass filters 30 and 31 to obtain an analog reproduced color-difference signal. Furthermore, the analog reproduced color-difference signal is modulated by a modulation device 32.
At this time, the switch circuits 25 and 26 are switched to the PB side, selecting the modulated analog reproduced color-difference signals together with the analog reproduced luminance signal, and output these signals as a reproduced video signal.
In the case of the conventional digital video camera apparatus shown in FIGS. 1A and 1B, in order to allow recording/reproduction of both digital luminance and color-difference signals from the camera and external analog luminance and color-difference signals, many A/D converters, D/A converters, and the like are required. For this reason, the circuit scale constituting the digital video camera apparatus becomes large, and it is difficult to reduce cost.
In conventional image pickup recording apparatuses adopting a digital signal processing system, an image pickup signal processing circuit is an analog circuit, and an output signal from the analog processing circuit is converted into a digital signal. For this reason, due to a large circuit scale, the number of components becomes large, and current consumption undesirably increases. Also, it is difficult to make the apparatus compact, and to reduce cost.
Since the apparatus includes both an analog signal processing circuit and a digital signal processing circuit, a sufficient S/N ratio cannot often be obtained due to interference such as mixing of a digital signal into an analog signal, and the apparatus cannot be rendered compact.
Since the image pickup signal processing circuit adopts analog processing, image quality is determined by performance such as the frequency characteristics, noise characteristics, a change in performance due to a change in temperature, a variation in characteristics in units of circuits, and the like, and it is difficult to achieve high image quality.
In order to attain special effects using a frame memory and a digital calculation, a still larger number of circuit components are required. As a result, it is difficult to make the apparatus compact, and power consumption undesirably increases.